The present invention relates to softball and baseball bats and more particularly relates to bats formed at least in part from a composite material(s).
Recent years have seen an emergence of new and improved tubular metallic softball and baseball bats. The most common tubular bat is the aluminum single-wall tubular bat. Such bats have the advantage of a generally good impact response, meaning that the bat effectively transfers power to a batted ball. This effective power transfer results in ball players achieving good xe2x80x9csluggingxe2x80x9d distances with batted balls. An additional advantage of such aluminum bats is the improved durability over crack-prone wooden bats.
Despite the advantages of tubular aluminum bats, there is an ongoing effort to improve the performance and durability of the conventional design. Generally speaking, bat performance is a function of the weight of the bat, the size of the hitting area or xe2x80x9csweet spotxe2x80x9d of the bat, and the impact response of the bat. The durability of a bat relates, at least in part, to its ability to resist denting and depends on strength and stiffness of the tubular frame. While recent innovations in bat technology have increased performance and durability, most new bat designs typically improve performance or durability at the expense of the other because of competing design factors. For example, an attempt to increase the durability of the bat often produces an adverse effect on the bat""s performance.
More specifically, the impact response of a bat depends on the bat wall""s elasticity, rebound recovery time, and rebounding force. Generally, impact response is optimized when the bat undergoes maximum elastic deflection and then rebounds with the greatest force in the shortest amount of time. The elasticity of a bat can be increased by reducing the thickness of the bat""s tubular frame. In contrast, the durability of a bat generally is improved by increasing the thickness of the tubular frame. Consequently, a bat having a relatively thin tubular wall is capable of large elastic deflection, but may be vulnerable to undesirable local plastic deformation (or xe2x80x9cdentingxe2x80x9d). On the other hand, a relatively thick tubular wall is more durable but may be too stiff to achieve optimum slugging performance. Thus, enhancing one design aspect of a bat often compromises another.
Another example of competing design factors concerns the bat""s optimum hitting area or xe2x80x9csweet spot.xe2x80x9d The sweet spot is typically located near the center of the impact area of the bat. The performance of the bat drops off considerably when a ball impacts the bat outside the sweet spot, for example, near the end of the bat. When this occurs, the batter feels greater vibrations and transfers less energy from the bat to the ball. An obvious way to increase the sweet spot of a bat is to increase the length and circumference of the bat. This option is constrained by institutional rules and regulations. In addition, an increase in the overall size of the bat undesirably adds weight, often causing reduced bat speed and less slugging distance. (A hitter often can increase bat speed by using a lighter bat, thereby increasing the force transferred to the ball upon impact.
An example of a bat incorporating a composite insert is shown in U.S. Pat. No. 5,364,095. This patent discloses a tubular aluminum bat having a carbon composite insert to increase the xe2x80x9cstiffnessxe2x80x9d of the metal tube. The insert is made of multiple fiber layers, each layer having bidirectional woven fibers directed at 0 and 90 degrees relative to the axis of the bat. The insert is bonded to the barrel portion of the surrounding metal tube or frame and presses outwardly on the frame to produce a pre-load stress of several thousand pounds per square inch. The insert appears to be formed from multiple layers of glass and carbon fiber material (thickness of 0.03 to 0.05 inch) so as to be a self-supporting structure capable of withstanding several thousand pounds of compressive stress. This design gives the bat a relatively stiff, rigid tubular frame which appears to be capable of limited elastic deformation, a less than ideal trait if the goal is to optimize slugging performance. (One would expect this design to behave like a single-wall bat in which the compressive stress must be overcome before the wall begins to deflect.)
While composite materials offer the advantage of a high strength to weight ratio, such materials also present design challenges. Composite inserts and bat frames are prone to wear and tear due to the inter-laminar shear which can occur between bonded layers of composite material. The deflection caused when a ball impacts the bat produces shearing stresses between the composite layers, sometimes causing the bond between adjacent layers to fracture or separate (especially over time). When this occurs, the bat""s performance deteriorates. This is particularly disadvantageous when one considers the relatively high cost of manufacturing composite inserts.
Thus, despite the advantages offered by composite materials, there are two constraints associated with using such materials: a reduced elastic deflection potential which compromises bat performance and a tendency of the composite layers to separate over time due to inter-laminar shear.
As a result, there is a need for a tubular bat that offers at least some of the advantages of composite materials without the constraints. There is a need for a tubular bat that provides excellent slugging performance and improved durability. There also is a need for a multi-wall bat which has a relatively thin barrel wall and yet exhibits excellent durability. Further, there is a need for a single wall bat having the excellent durability characteristic of most single wall bats as well as improved slugging performance.
The present invention provides an improved baseball or softball bat with superior durability characteristics and little or no reduction in bat performance. The invention does so by providing a relatively thin, light (but strong) composite material, with directional strength characteristics to resist dent-causing forces, in bonded relationship to a metal carrier. For example, the present invention includes a single- or multi-wall tubular bat having at least one composite layer, with its greatest strength in a substantially circumferential direction, bonded directly to a tubular member which deflects upon ball impact.
In one embodiment, the bat has a tubular frame and a tubular insert reinforced with at least one composite layer. The composite layer has its greatest strength in a substantially circumferential direction and is bonded to at least a portion of the outer surface of the insert. The composite layer provides several advantages, including improved durability with little or no reduction in performance. Because the composite layer adds strength and stiffness to the insert in the circumferential direction, it helps prevent local plastic deformation caused by circumferential stresses while allowing the frame and insert to deflect sufficiently in the axial direction to transfer substantial energy back to the ball as it leaves the surface of the bat. In another embodiment, the composite layer(s) is bonded to at least a portion of the inner surface of the insert.
The present invention also contemplates the use of multiple composite layers of varying lengths and different strength characteristics bonded to the impact portion and/or the insert of a bat so that a manufacturer can add strength and stiffness to a bat where it is needed and in the direction that it is needed. Because the intended use of a bat often drives its design, the various attributes of the composite layers, such as length, thickness, location on a bat, or orientation of fibers, may be selected to suit a particular application.
Another embodiment, which exhibits excellent durability and performance characteristics for hitting a softball, has two composite layers bonded to the outer surface of a tubular sleeve. A longer, first composite layer having its fibers oriented substantially at 0 degrees relative to the axis of the bat is applied directly to the outer surface of the sleeve. A shorter, second composite layer having its fibers oriented substantially at 90 degrees relative to the axis of the bat is placed on top of the first layer, with the second layer being positioned closer to the xe2x80x9csweet spot.xe2x80x9d
Various advantages and features of novelty which characterize the invention are particularized in the claims forming a part hereof. However, for a better understanding of the invention and its reference should be had to the drawings and to the accompanying description in which there is illustrated and described preferred embodiments of the invention.